Removal of synthetic dyes from wastewaters: a review.

Laccases of fungi attract considerable attention due to their possible involvement in the transformation of a wide variety of phenolic compounds including the polymeric lignin and humic substances. So far, more than a 100 enzymes have been purified from fungal cultures and characterized in terms of their biochemical and catalytic properties. Most ligninolytic fungal species produce constitutively at least one laccase isoenzyme and laccases are also dominant among ligninolytic enzymes in the soil environment. The fact that they only require molecular oxygen for catalysis makes them suitable for biotechnological applications for the transformation or immobilization of xenobiotic compounds.

Fungal laccases - occurrence and properties.

Immobilization is often the key to optimizing the operational performance of an enzyme in industrial processes, particularly for use in non-aqueous media. Different methods for the immobilization of enzymes are critically reviewed. The methods are divided into three main categories, viz. (i) binding to a prefabricated support (carrier), (ii) entrapment in organic or inorganic polymer matrices, and (iii) cross-linking of enzyme molecules. Emphasis is placed on relatively recent developments, such as the use of novel supports, e.g., mesoporous silicas, hydrogels, and smart polymers, novel entrapment methods and cross-linked enzyme aggregates (CLEAs).

http://largens.com/biochemlab/peroxidase2.pdf

Enzyme immobilization: The quest for optimum performance

With the approaching commercialization of PEM fuel cell technology, developing active, inexpensive non-precious metal ORR catalyst materials to replace currently used Pt-based catalysts is a necessary and essential requirement in order to reduce the overall system cost. This review paper highlights the progress made over the past 40 years with a detailed discussion of recent works in the area of non-precious metal electrocatalysts for oxygen reduction reaction, a necessary reaction at the PEM fuel cell cathode. Several important kinds of unsupported or carbon supported non-precious metal electrocatalysts for ORR are reviewed, including non-pyrolyzed and pyrolyzed transition metal nitrogen-containing complexes, conductive polymer-based catalysts, transition metal chalcogenides, metal oxides/carbides/nitrides/oxynitrides/carbonitrides, and enzymatic compounds. Among these candidates, pyrolyzed transition metal nitrogen-containing complexes supported on carbon materials (M–Nx/C) are considered the most promising ORR catalysts because they have demonstrated some ORR activity and stability close to that of commercially available Pt/C catalysts. Although great progress has been achieved in this area of research and development, there are still some challenges in both their ORR activity and stability. Regarding the ORR activity, the actual volumetric activity of the most active non-precious metal catalyst is still well below the DOE 2015 target. Regarding the ORR stability, stability tests are generally run at low current densities or low power levels, and the lifetime is far shorter than targets set by DOE. Therefore, improving both the ORR activity and stability are the major short and long term focuses of non-precious metal catalyst research and development. Based on the results achieved in this area, several future research directions are also proposed and discussed in this paper.

A review on non-precious metal electrocatalysts for PEM fuel cells

http://files.aprendiendoquimica7.webnode.com.co/200000006-1247d13423/Limousin,%20G%20et%20al.%20Sorption%20Isotherms%20A%20review%20on%20Physical%20Bases,%20modeling%20and%20measurement.pdf

Sorption isotherms: A review on physical bases, modeling and measurement

White-rot fungi were studied for the decolorization of 23 industrial dyes. Laccase, manganese peroxidase, lignin peroxidase, and aryl alcohol oxidase activities were determined in crude extracts from solid-state cultures of 16 different fungal strains grown on whole oats. All Pleurotus ostreatus strains exhibited high laccase and manganese peroxidase activity, but highest laccase volumetric activity was found in Trametes hispida. Solid-state culture on whole oats showed higher laccase and manganese peroxidase activities compared with growth in a complex liquid medium. Only laccase activity correlated with the decolorization activity of the crude extracts. Two laccase isoenzymes from Trametes hispida were purified, and their decolorization activity was characterized.

Industrial Dye Decolorization by Laccases from Ligninolytic Fungi

Polycyclic aromatic hydrocarbons (PAHs) are pollutants that are found in most terrestrial environments (8, 9). Many fungi can metabolize PAHs by using either a cytochrome P-450 monooxygenase system (2, 22) or, in the case of white rot fungi, lignin peroxidase or related enzymes (22). In organisms that use the cytochrome P-450 system, the trans-dihydrodiol product cannot be used as an energy source, although further metabolism may occur. However, in white rot fungi, such as Phanerochaete chrysosporium, and in Trametes versicolor, mineralization of some PAHs occurs, indicating that complete breakdown of PAHs occurs (21, 22). Fewer examples of in vitro oxidation of PAHs by culture supernatants and purified enzymes have been described, although oxidation of anthracene and pyrene by lignin peroxidase and manganese peroxidase from P. chrysosporium (7, 11, 24) and oxidation of many PAHs by the laccases of T. versicolor (5, 10, 13, 17) have been reported. Manganese peroxidases from Phanerochaete species can also be involved in PAH metabolism (3, 4), and recently a manganese peroxidase preparation from Nematoloma frowardii has been implicated in direct mineralization of aliphatic and aromatic compounds, including pyrene (12).

White rot fungi also can metabolize specific polychlorinated biphenyl (PCB) congeners (1). In the study of Beaudette et al. (1) a number of previously uncharacterized fungi were screened for PCB metabolism and mineralization. Under the conditions used, significant levels of PCB metabolism (87 to 93%) and mineralization (4.7 to 11.1%) were observed in strains of T. versicolor and Bjerkandera adusta but not in P. chrysosporium. Our objectives in this study were (i) to determine if previously uncharacterized fungal strains could metabolize selected PAHs in vivo and (ii) to study PAH metabolism by using partially purified enzymes in vitro. Our long-term goals are to chemically modify PAH-metabolizing enzymes in order to enhance their activities in organic solvents (23–25) and to identify fungal strains that can produce high levels of lignin-degrading enzymes and enzymes with enhanced stability to pH and temperature or with high levels of activity in organic solvents.

/pdf/polycyclic-aromatic-hydrocarbon-metabolism-by-white-rot-dy0dlvbnrv.pdf

Polycyclic Aromatic Hydrocarbon Metabolism by White Rot Fungi and Oxidation by Coriolopsis gallica UAMH 8260 Laccase

It has been proposed that addition of surfactants to contaminated soil enhances the solubility of target compounds; however, surfactants may simultaneously reduce the adhesion of bacteria to hydrophobic surfaces. If the latter mechanism is important for the biodegradation of virtually insoluble contaminants, then the use of surfactants may not be beneficial. The adhesion of a Mycobacterium strain and a Pseudomonas strain, isolated from a creosote-contaminated soil, to the surfaces of highly viscous non-aqueous-phase liquids (NAPLs) was measured. The NAPLs were organic material extracted from soils from two creosote-contaminated sites and two petroleum-contaminated sites. Cells suspended in media with and without surfactant were placed in test tubes coated with an NAPL, and the percentages of cells that adhered to the surface of the NAPL in the presence and absence of surfactant were compared by measuring optical density. Test tubes without NAPLs were used as controls. The presence of either Triton X-100 or Dowfax 8390 at a concentration that was one-half the critical micelle concentration (CMC) inhibited adhesion of both species of bacteria to the NAPLs. Both surfactants, when added at concentrations that were one-half the CMCs to test tubes containing previously adhered bacteria, also promoted the removal of the cells from the surfaces of the NAPL-coated test tubes. Neither surfactant was toxic to the bacteria. Further investigation showed that a low concentration of surfactant also inhibited the growth of both species on anthracene, indicating that the presence of a surfactant resulted in a reduction in the uptake of the solid carbon source.

Bacterial adhesion to soil contaminants in the presence of surfactants

Laccase from Coriolopsis gallica UAMH8260 was immobilized on activated agarose and tested for repeated decolorization of industrial dyes. Immobilized enzyme retained 85% of the initial activity after 10 cycles, and 70% after 3 months of intermittant use in the decolorization of Reactive Blue 198 dye. Free laccase decolorized 13 of 38 industrial dyes tested but, in the presence of 1 mM 1-hydroxybenzotriazole as a free radical mediator, the enzyme decolorized 26 of the 38 dyes increasing both the range and rate of decolorization. Immobilized laccase showed a higher thermal stability at 70 °C than free enzyme but no increased resistance to organic solvents.

Hydroxybenzotriazole increases the range of textile dyes decolorized by immobilized laccase

The mechanism of transport of polycyclic aromatic hydrocarbons (PAHs) by Pseudomonas fluorescens LP6a, a PAH-degrading bacterium, was studied by inhibiting membrane transport and measuring the resulting change in cellular uptake. Three cultures were used: wild-type LP6a which carried a plasmid for PAH degradation, a transposon mutant lacking the first enzyme in the pathway for PAH degradation, and a cured strain without the plasmid. Washed cells were mixed with aqueous solutions of radiolabelled PAH; then the cells were removed by centrifugation, and the concentrations of PAH in the supernatant and the cell pellet were measured. The change in the pellet and supernatant concentrations after inhibitors of membrane transport (azide, cyanide, or carbonyl cyanide m-chlorophenyl hydrazone) were added indicated the role of active transport. The data were consistent with the presence of two conflicting transport mechanisms: uptake by passive diffusion and an energy-driven efflux system to transport PAHs out of the cell. The efflux mechanism was chromosomally encoded. Under the test conditions used, neither uptake nor efflux of phenanthrene by P. fluorescens LP6a was saturated. The efflux mechanism showed selectivity since phenanthrene, anthracene, and fluoranthene were transported out of the cell but naphthalene was not.

https://aem.asm.org/content/aem/66/12/5387.full.pdf

Michael A. Pickard

Papers

Industrial Dye Decolorization by Laccases from Ligninolytic Fungi

Polycyclic Aromatic Hydrocarbon Metabolism by White Rot Fungi and Oxidation by Coriolopsis gallica UAMH 8260 Laccase

Bacterial adhesion to soil contaminants in the presence of surfactants

Hydroxybenzotriazole increases the range of textile dyes decolorized by immobilized laccase

Uptake and active efflux of polycyclic aromatic hydrocarbons by Pseudomonas fluorescens LP6a.